A primary objective of the research program is to examine the hypothesis that the anatomical and physiological development of the brainstem auditory system result in some measure from interactions between pathways conveying information from each ear. How, for example, will brainstem auditory pathways develop in an animal deprived from birth of sensory information from one ear? The physiology of the inferior colliculus and the composition of its afferent projections from brainstem auditory neclei will be studied. Three specific questions about these developmental interactions are (1) whether the ubiquity of ipsilaterally evoked excitation in the inferior colliculus is limited by contralateral pathways, (2) whether ipsilateral responses of single neurons in the central nucleus of the inferior colliculus depend upon the integrity of contracteral pathways, and (3) whether interactions between auditory brainstem pathways during development determine the connectivity of the inferior colliculus bilaterally with brainstem auditory nuclei. The physiology of the inferior colliculus will be studied using single and multiple unit techniques in normal animals and in animals subjected at neonatal or later ages to unilateral destruction of the cochlea. Anatomical changes that result from these cochlear ablations will be studied using retrograde transport techniques. This research is pertinent to understanding both the physiological and anatomical consequences of perinatal destruction of the cochlea in humans, as frequently occurs, for example as a consequence of maternal rubella. The second objective of the research is to study the functional development of the cochlea in an age-graded series of gerbils. The objectives are to (1) determine whether the resonant properties of the basilar membrane change systematically as the transducer system matures, (2) examine the functional development of different turns of the cochlea and (3) relate to development of the middle ear transfer function to the maturation of cochlear responsiveness.